70 ECONOMIC ESSAYS IN HONOR OF JOHN BATES CLARK
tion.® Such verification will, of course, always reveal the presence
of other forces than the purely static ones, modifying the results
in any given case. Inductive studies will deal, not only with the
trend-values around which actual values fluctuate, but also with
the forces setting limits on their oscillations. Here the static
forces, corresponding to the force of gravity in mechanics, are at
work, but under conditions which differ from the complete static
picture, and require correspondingly different methods of study.
And finally, in the inductive study of actual conditions, there
will always arise the difficulty that a mere description of facts
does not afford an explanation or interpretation of them. The
question will still remain why they behave as they do. And here
again the static approach will prove useful and effective, chiefly
in the form of inverse deduction, which has already been men-
tioned. The reasoning takes the following form. If the facts
were found to behave in certain simple ways, we should infer the
presence of static forces only, acting under static conditions only.
Since the facts behave differently, we infer the joint action of
static and dynamic forces, and attribute the departures from the
static model to the dynamic elements in the situation. And the
nature of these departures are, if properly understood, such as we
should expect from the nature of the dynamic forces. Thus brief
reversions to the static method of isolation will help us to
separate out the forces acting under actual conditions, and to
make of dynamics an explanation, rather than a mere description
of economic behavior.
1 See “Partial Elasticity of Demand,” Quar. Jour. Econ. XL, 393-401,
May, 1926; “A Theory of Economic Oscillations,” XLI, 1-29, Nov., 1926.